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From: "Sandy, W5TVW"
To: "Elecraft Reflector"
Date: Thu, 13 Jun 2002 21:25:15 -0500
Subject: [Elecraft] K1- VFO "jump"
A problem cropped up with my K1 a couple of days ago. The frequency of the
VFO "jumped" a small amount, perhaps 50-150 Hz. from time to time. If the
set was tapped on with the finger smartly, it would "jump" as much as 200 Hz.
The amount of the "jump" would be erratic from occurrence to occurrence.
I found that the VFO oscillator toroid was "cocked" on the lower
nylon washer (next to the PC board.) I was apprehensive that the washer
wasn't quite large enough in diameter and lacked a "shoulder" to centralize
the core when I assembled it, and proceeded on nevertheless.
I dug a fibre washer (like the kind used on binding posts) out of my
hardware junkbox that had a raised "shoulder" on it that was just
right for the toroid core and fit the mounting screw. It kept the
toroid core from "cocking" off center when the nylon screw was tightened.
I installed it in place of the lower nylon washer, and respaced the
windings on the VFO core to get the desired tuning range coverage
on all 4 bands from 40-15 meters. This seems to hold the core
central to the mounting screw and I think it will solve my problem.
Has anyone else noted this on their K1's? I can supply a scanned
drawing of this, but didn't attach it, as on many reflectors, attachments are
banned or truncated from the messages posted.
73,
Sandy W5TVW
K1 #1178
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Date: Wed, 28 May 2003 12:40:04 -0700
From: Wayne Burdick
Organization: Elecraft
To: Elecraft
Subject: [Elecraft] K1 RIT and VFO counter hysteresis
There has been some discussion lately about a change in the K1's displayed VFO
frequency on exit from RIT mode. This is due to our use of "hysteresis"
(lead/lag updates) in the K1's VFO frequency counter firmware. Applying
hysteresis prevents flickering of the 100 Hz digit on the LCD. But as a
side-effect, a shift of as much as 200 Hz is possible when changing bands or
turning RIT on/off.
For those of you who are still awake :) here is further and still more arcane
detail: Suppose, due to the hystereis algorithm, you had a "lead" of one count
(100 Hz) in one direction at the time RIT is turned on. By the time it is turned
off, the counter will have sampled again many times, and it could now exhibit a
"lag" of 100 Hz in the other direction. The net (200 Hz) represents the
worst-case shift that you would ever see, assuming that VFO drift during the
interval is less than 100 Hz.
It would be possible to change the firmware to catch this condition explicitly
and guarantee that you'd never see the 200 Hz apparent frequency shift. But the
truth is that the display is still accurate to within +/- 100 Hz even in this
case, which meets the intended spec for the K1 VFO. And of course the VFO itself
will exhibit no shift at all--it's just the display that changes.
So I think we'll reserve the firmware space for something more interesting!
73,
Wayne
N6KR
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